Apparatus for drying wood



Feb. 27, 1951 H. P. woon APPARATUS FOR DRYING WOOD 4 Sheets-Sheet 1 Original Filed Dec. 19, 1946 N \n INVLZY TOR. M 79 .BY 4 I ATTORNEY Feb. 27, 1951 H. P. WOOD 2,543,618

APPARATUS FOR DRYING woon Original Filed Dec. 19, 1946 4 Sheets-Sheet 2 43 44 FIG. 5

IN VEN TOR.

/W ATTORNEY FIG. 4

Feb. .27, 1951 'H. P. WOOD I 2,543,613

APPARATUS FOR DRYING wooo Original Filed Dec, 19, 1946 4 Sheets-Sheet 3 IN VEN TOR.

ATTORNEY H. P. WOOD APPARATUS FOR DRYING WOOD Feb. 27, 1951 4 Sheets-Sheet 4 Original Filed Dec. 1946 .mdE

ON 2 m E w E E m m O m m N w o v n m Q o INVENTOR.

ATTORNEY Patented Feb. 27, 1951 APPARATUS FOR DRYING Harold 1'. Wood, North Berwlek, Maine, signer to Wood Electro Process Company, South Berwlck, Maine, a corporation of Maine Original application December 19, 1940, Serial No.

Divided and this application March 31, 1948, Serial No. 18,277

4 cam (Cl. 34-1) This invention relates to a method of and an moisture laden wood and, more particularly, wood in the form of lumber.

This application is a division of my application Ser. No. 717,207, filed December 19, 1946.

It has long been known that a large mass of green lumber could be dried by subjecting it to heated air and that a small quantity of wood could be dried by subjecting it to high frequency electric power.

However, a relatively long time, approximately one week, is required to dry green lumber by heated air and frequently such lumber so dried is discolored not only by the distillation of the pitch content thereof, but also by the creation of a grayish-blue mold or fungus growth on its surfaces which must be planed off before the lumber is suitable for use.

The cost of drying a large mass of green lumber by high frequency power is prohibitively high and is not commercially practicable, because, among other reasons, green lumber has a high moisture content and.therefore a high dielectric constant, the dielectric constant of the lumber is the dielectric will be of relatively apparatus for drying large masses of green I large capacitance and its circuit will have a high power factor. This will result in an enormous dissipation of power for many hours until the moisture content of the lumber has been materially reduced. Even if the wood is not dried by the application of high frequency power alone, but by the use of high frequency power and heated gas simultaneously, the result will not be substantially different from that above set out. The cost of drying a large mass of green lumber by high frequency power alone or by high frequency power and heated gas simultaneously would greatly exceed that of drying it by the methods now employed which involve the use of heated air alone. Furthermore, the resulting rapid evaporation of moisture will build up internal pressures which rupture, check and distortthe lumber. Moreover, the internal heat developed in the lumber will cause discoloration of the surfaces of the boards by blackening the pitch pockets.

I have discovered, however, that alarge stationary mass of completely enclosed green lumber may be partially dried by subjecting it to a current of heated gas, preferably air, for a relatively short time, for example, eight hours, without blackening the pitch pockets, or creating mold or fungus on the surfaces thereof, and that 2 the moisture content of the lumber may then be reduced to a percentage within the range of the moisture content of commercial dried lumber by subjecting it to high frequency electric power and preferably a current of heated gas simultaneously with the electric power treatment for a relatively shorter length. of time, for example, four hours, without distortion or discoloration of the lumber. My tests were made with white pine. For harder woods, the time factors would be somewhat different but always the period of the application of the electric power will be much shorter than that of the application of the heated gas.

One of the many advantages and useful results secured by my method is that lumber treated in this manner will not thereafter develop mold or fungus on its surface, for the rea son that the temperature to which the lumber is raised by the high frequency power, is suflicient to kill, and therefore prevent further growth of, the spores latent in the wood from which the mold or fungus is created.

It is therefore the principal object of my in-- vention to provide a method of and an apparatus for drying alarge mass of green lumber, first, by subjecting it to a current of heated gas for a suflicient length of time to reduce the moisture content thereof without distortion or discolorationand then subjecting it to high frequency electric power for a sufficient length of time, shorter than that of the heated gas treatment, to reduce the moisture content of the lumber to a percentage within the range of the moisture content of commercial dried lumber without distortion or discoloration, whereby the time required for drying green lumber, and the expense thereof, are greatly reduced.

While, preferably, the first step of my method may be performed by the apparatus herein described, or any suitable equivalent thereof, it is feasible partially to dry a large mass of green lumber in any of .the ways now employed for this purpose, for example, by subjecting it to heated air in a kiln at the usual progressively increasing temperatures for the usual time, say, about one week, or subjecting it to .the atmosphere and sun for about one year. Lumber so treated usually is discolored as aforesaid.

It is therefore another object of my invention to provide a method of and an apparatus for drying a large mass of partially dried lumber, such as kiln dried or air dried lumber, by sub- Jecting' such mass to high frequency electric power for a length of time sufficient to reduce aea'aeie the moisture content thereof to a percentage within the moisture content of commercial dried lumber and simultaneously subjecting the same to a current of heated gas, such as air, having a temperature low enough to prevent the temperature of the lumber due to the combined action of the electric power and heated gas from rising high enough to cause discoloration, or further discoloration, as the case may be, but the heated air should have a temperature high enough to prevent a substantial amount of the heat in the lumber from escaping. The time for producing commercial dried lumber in this manner is much longer than that required by my preferred method above stated. and the lumber, if affected by the mold aforesaid, must. either prior to the application of the electric power, or at the end of such process, be planed to a depth of about /soth of an inch.

A further object is the provision of an apparatus whereby my improved method may be practiced in such manner as greatly to reduce the cost of producing commercially acceptable dried lumber and the time required to produce it.

Other objects will appear from the appended claims and the detailed description of the drawings which illustrate one of the many forms of apparatus and circuit arrangements whereby my method may be realized in practice, it being understood, of course, that said method is broader than mere apparatus and may be realized by a variety of means.

In the drawings accompanying and forming a part of this specification,

Figure 1 is a plan view.

Fig. 2 is a longitudinal vertical section taken on the line 2-2 of Fig. 1.

Fig. 3 is a transverse vertical section taken on the line H of Fig. 1.

Fig. 4 is a horizontal section taken on the line 4-4 of Fig. 3.

Fig. 5 is a sectional view on an enlarged scale, partly elevationai and partly schematic. showing one way in which the humidity of the heated gas in each of the compartments may be controlled.

Fig. 6 is a sectional view on an enlarged scale taken on substantially the same plane as Fig. 2.

Fig. 7 is a fragmentary section partly in elevation, taken on the line of Fig. 6.

Fig. 8 is an isometric view, representing schematically the relative positions of the electrodes and their connection to the source of high frequency power.

Fig. 9 shows a family of curves drawn to rectilinear coordinates illustrating the variation of the moisture in the wood with the periods of application of the heated gas and the high frequency electric power.

In the particular drawings selected for more fully disclosing my invention, and the underlying principles thereof, said drawings being illustrative, merely, and not restrictive, 20 is a heat insulated, continuous, longitudinally extending chamber having movable end closures 2i, 2!, shown, in the present instance, as vertically movable doors guided by the channels 23, and movable partitions 24, 25, intermediate the ends of the chamber for dividing the same into communicating compartments, herein shown-as three, said compartments being identified by the refer ence numerals 26, 21, 28, respectively. The movable partitions may be doors, each having a number of hingedly connected sections commonly known as garage doors," each section being provided with rollers 20 enclosed within the usual guides 8. (Figs. 6 and 'l). leans preferably are employed for operating said doors from the exterior of the chamber and. in the present instance.theoperatingmeansareshownasa cable It trained around the sheaves J! and havingitsendsconnectedtotherespective ends of the door whereby an operative on the roof of the chamber may move the partitions to operative or vertical position. as indicated at the left end of compartment 21 in Fig. 2 or horizontal or inoperative position as shown at the right end of said compartment.

Each compartment is provided with louvres it that may be controlled in any suitable manner. as, for example, the rods 84 each provided with ahandpiece II at its upperend. Itis to beunderstood, of course, that any suitable means may be employed for varying the temperature of the heated gas supplied to each compartment, as well as the amount thereof.

For supplying heated gas, preferably air, to each compartment, there is provided a suitable source of such gas or air indicated at It, each said source being connected to one of said compartments by a supply conduit 31, preferably controlled by a valve II, and an exhaust conduit is, suitable means, such as the blower it being provided to draw the heated gas from its source and return it thereto. The velocity of the heated gas through each compartment will of course be controlled by the speed of the blower, and said louvres.

The humidity of the heated gas in each compartment may be controlled by any suitable type of humidistat and a ventilator or other means controlled thereby. In the present instance, a humidistat 4| is placed in the interior of each compartment and may be supported by the frame 4| depending from the roof thereof. A small source of electromotive force, such as a one cell battery ll, is controlled by the humidistat to energize or deenergize the relay 4!, the armature of which controls the circuit of the solenoid 43. which includes the battery or other suitable source of electromotive force 44 that is larger than that of the source II. By suitable connections. the core ll of the solenoid will actuate a suitable ventilator. such as that shown at It.

A pair of rails 41 are laid on the bottom of the continuous chamber and extend a suitable distance beyond the ends thereof. A truck or trucklike carrier for moving the lumber to be treated into or out of said chamber and through the several compartments thereof is mounted on the wheels 48, which preferably are provided with double flanges. In the present instance, a plank 49 is placed longitudinally acrossthe bifurcated member It in the depending sides of which said wheels are journalled. and a series of planks II are placed transversely across the pair of planks 49. It is to be understood. of course. that any suitable form of wheeled carrier. such as a truck, may be employed in place of the "dolly" above described.

Upon the trucklike carrier, the lumber to be treated is placed, the boards 52 being spaced by sticks 53.

Any suitable means may be employed for moving the trucklike carriers with their respective loads of lumber through the continuous chamber, and, preferably, such means must be of such nature asto co-operate with the movable partitions 14, It, in such manner that it is only when the latter are in inoperative position that a load of lumber can be moved into or out of the middle compartment 21. In the present instance, I have shown a continuous band means in the form ofendless chain 66 trained around a sprocket 66 at the forward end of the chamber and around a sheave 66 at the rearward end thereof. Secured to and projecting from the outer face of each member 60 is a saddle 61 so disposed as to cooperate with said chain when either of the partitions 24, 26, is in elevated or inoperative position, but when said partitions are in vertical or operative position, portions of the chain or band means will be depressed and thereby uncoupled from the saddle.

Th door 24 is never opened until after the truck and its completely treated load of lumber in compartment 26 have been moved out of said compartment and the door 2i has been closed.

In such case, the door 24, being raised, the heat in chamber 21 is not lost but is distributed'between compartments 26 and 21 so that when the truck and its load of lumber are moved out of compartment 21 to compartment 26 and the door 24 is again closed preparatory to the treatment of the lumber in compartment 26 with high fre: quency power and heated gas, the load in compartment 26 would not be subjected to the effects of the outside unheated air. In like manner, the door 25 is never raised until a load of lumber has been drawn into compartment 26 and the end door 22 closed. when in the course of the process, it is desired to move a load from compartrnent 26 to compartmentfl, the door 25 is raised and the chain brought into co-operation with the saddle 51 of the truck which at that time is in compartment 26, whereupon said load will be drawn into compartment 21 without any dissipation of heat, the doors 26 and 22 both being closed.

Near the top of chamber 26 is disposed a vertically movable electrode 62, such electrode preferably being formed by heavy wire mesh and supported by channels or other suitable members 63.

By means of the rods 66, each provided with a hand piece 66, and secured to said channels by the cross rods 66, the electrode 62 may be elevated or depressed in accordance with the height of the load of lumber with which it is to co-operate. A similar electrode 61 is placed on the trucklike carrier and, in the present case, where such carrier is a dolly, said electrode will rest on the transverse planks 6|. Thus, the electrode 61 is disposed between the carrier and the wood. Generally speaking, a third electrode 66 will be employed and disposed in contact with the wood approximately midway between the other two. This electrode also will be disposed between the carrier and the upper section of the lumber.

In order to secure a uniform electric field, the outer edges of all electrodes should extend substantial distances beyond the edges of the lumber to be treated (62', 61', 66, Figs. 2 and 8).

In order to connect the electrodes to the source of high frequency power, brushes, preferably of resilient material, may be disposed in the chamber 26 in such position as to co-operate with the edges of the electrodes. In the present instance, I have shown three such brushes 69 attached to the wall of chamber 26, each being formed of resilient material and'consisting of a curvilinear sheet of substantial height, as shown in Figs. 3 and 4, in order to accommodate themselves to the varying distances above the base of the chamber of the three electrodes. If three electrodes are employed, one of them for example, the

6 center electrode, is connected to one terminal II of the source of high frequency electric power Ii by the lead 12, and the other two are connected together by the lead 12 and the latter connected by the lead II to the other terminal I6 of said source.

In order to prevent the radiation of high frequency electric waves, the chamber 26 and the source of high frequency power H, are both shielded by suitable shields I6, 11, which shields may be copper mesh or metal coated paper or the like.

While, as hereinbefore stated, my method may be practiced by a variety of means, I have described in some detail an apparatus by mean of which my process may be carried out on a commercially profitable scale. It is to be understood, however, that all constants and magnitudes, such as the number of compartments into which the chamber is divided, the temperature of the heated gas to which the lumber is subjected, the frequency of the high frequency power, the wattage thereof applied to the lumber, and'the amount of lumber treated, are given merely by way of examples, and are not to be considered as limitations of the process or apparatus.

By means of the apparatus described, 4000 board feet of green moisture laden lumber may be dried in 12 hours and converted into "commercial dried lumber having a moisture content between 4% and 15%. the moisture content of green or freshly cut pine as it comes off the saw mill being taken as (see Fig. 9). At the end of every four-hour period following the first 12- hour period, 4000 more board feet will be commercially dried, making in all, 16,000 board feet for the first day's operation of 24 hours. On the second and following days, 4000 board feet of green lumber may be converted to commercial dried lumber every four hours, making an output of 24,000 board feet per dayof 24 hours.

I have illustrated a continuous chamber divided into three compartments, each capable of treating 250 boards, each 1 foot wide, one inch thick and 16 feet long, each such board containing 16 board feet. In each chamber, therefore, there will be 2500f such boards and, in such case, the third or intermediate electrode 68 will be desirable if the voltage of the high frequency generator does not exceed about 10,000. There will then be about boards or about 2000board feet on each truck between the electrodes 61 and 66, and a like amount between the electrodes 62 and 66.

The temperature of the heated gas ought not to exceed approximately 225 F. and the velocity of the current of heated gas in the first chamber 26 may be about 200 feet per minute. The high frequency electric power of about 6.5 mc. per second applied to the wood in the third chamber may be about 20 watts per pound of the partially dried wood, and ought not to exceed 35 watts per pound of such wood. Any suitable type of high frequency oscillator having a rating of about 200 kw. may be used in the instant case.

The humidity in the first compartment 26 ought to have a range of from 50% to 80%; in the second compartment 21, between 20% and 50%; and in the third compartment 26, between 5% and 20%. The velocity of the current of heated air in the second and third compartment should be high enough to maintain the desired humidity. Thus, as the wood in compartment 21 is drier than the wood in the first compartment, the velocity of the current of heated air in compartment 21 may be higher than that of the current of heated air in compartment 20 and the velocity of said current in compartment 26, higher than that of the current in compartment 21.

As the discoloration of the wood due to heat treatment is a function of time as well as temperature. it follows that if the treatment of the lumber in each compartment exceeds four hours, the temperature of the heated air may be lower than 225 without causing discoloration and also that if the time of treatment is less than four hours, the temperature of the heated air may exceed 225'.

It is of course not essential that three compartments should be used, for obviously my process could be carried out on a smaller scale by the use of a single compartment, such as the third compartment 20, in which case, the wood would be placed in said compartment by any suitable means, the boards being separated to afford easy access of heated air and then treated for 8 hours with such heated air and at the end of that period, with high frequency electric power and heated air for four hours. In that way, if 4000 board feet were treated, the ouput would be only 8000 board feet in 24 hours.

In the form shown in the illustrated embodiment of my invention, the supply pipe 31 is represented as entering the space 18 formed in one of the walls of a compartment and the exhaust pipe 30, as communicating with a similar space ll in the opposite wall, the passage of the air from the pipe 31 into the compartment being controlled by the louvres 33, and the passage of the air out of the compartment being similarly controlled. This arrangement, although at times desirable. is not absolutely necessary, although, due to the varying moisture content of the different kinds of lumber treated, some means for controlling the temperature and velocity of the heated air is, generally speaking, highly desirable.

In carrying out the first step of my method, it is desirable to subject the lumber to a current of heated air having a substantial velocity, as distinguished from drying lumber by subjecting it to heated air which has no motion. By so doing, much time is saved and the danger of discoloration and distortion of the lumber is eliminated because, among other reasons, the vapor emanating from the wood is immediately blown off the surface thereof.

It will be noted that after four hours of treatment by a moving current of heated air, the rate of evaporation or reduction of moisture content of the wood shows a marked decrease (Fig. 9). As the wood becomes drier, its dielectric constant becomes smaller, the capacitance of the capacitor of which the wood is the dielectric, becomes smaller, the capacitive reactance, the reciprocal of the product of capacitance by the product of 21' by the frequency, becomes larger and the power factor, the cosine of the angle of advance, becomes smaller, whereas should such electric power be applied to green lumber, a much larger amount of power would be required on account of the higher power factor thus making the cost prohibitively high and commercially impracticable. It will be obvious, of course, that the mass of lumber to be dried and the electrodes 62,

. GI, 01, constitute a capacitor, the capacitance of which will vary directly with the area of the electrodes and the dielectric constant of the material placed between them, and inversely with the separation of each pair of electrodes 82, I, and

8 I1, 00 (Fig. 8). The dielectric of this condenser consists partly of air and partly of partially dried wood, including, of course, a certain amount of water. This condenser will be charged and discharged twice per cycle just like any condenser of the ordinary commercial type. For alternating current of the high frequency above specified, 6.5 mc., or, for that matter, even of a much lower frequency, the skin effect" will cause such current flow as may occur between each of said two pairs of electrodes above specified to be confined to the surface of the wood, the penetration being a small fraction of a millimeter, so that the heating effect of such conduction will be practically nil. The skin effect varies inversely as the conductivity of the substance through which the current flows. It has been found that for soft iron. the skin effect at a frequency of 1 million, is 0.005 mm. and as the electrical conductivity of partially dried wood is much lower than that of soft iron, it follows that the skin effect in the present case will be much less than 0.005 mm., so that the heating of the wood due to such conduction will be practically nil.

The charging currents (displacement currents) however, will cause molecular motion in the solid dielectric material placed between said electrodes and, in that way, a large amount of heat will be created in such material uniformly from surface to surface. The conductance of the wood diminishes with the moisture content thereof, therefore, high frequency electrical power may be applied to the wood economically to effect the necessary reduction in the moisture content of the lumber after eight hours treatment with heated air sutliciently to bring it within the range of the moisture content of commercial dry lumber without distortion or discoloration within a relatively short time. This is shown by the dotted line curves in Fig. 9. which indicate a very rapid rate of drying between the eighth and twelfth hour. Thus, it will be noted, with respect to the uppermost curve, that in four hours, from the 8th to the 12th hour, the moisture content has been reduced from about 48% to about 15%, while if the heated air treatment had been continued to the twentieth hour, without any application of the high frequency electric power, the moisture content would have been about 25%. In the lowermost curve, the moisture content of the wood is reduced from 23% to 3% by four hours application of the high frequency power, while if the heated air treatment alone had been continued to the twentieth hour, the moisture content of the wood would have been 13%.

It is necessary that the lumber be subjected to heated gas simultaneously with the application thereto of the high frequency electric power because, among other reasons, the temperature to which the lumber is raised by high frequency power in the second step of my process, is much higher than that to which the lumber is raised by the heated gas in the first step thereof, and, therefore, the circulation and recirculation of the heated gas through the spaces between the lumber while the latter is being subjected to high frequency power, prevents a rise in the temperature of the lumber sufficiently high to produce discoloration or distortion thereof. This current of heated gas also performs the same function that it effects in the first step, viz., carries away the vapors caused by the evaporation of moisture of the wood and tends to equalize the drying of the several boards. Another reason will be obvious from an inspection of Pig. 9 showing curves based on actual tests. and that is. that the time of reducing the moisture content to the percentage desired, is slightly reduced by the heated gas. For example, in the uppermost curve, the effect of the heated gas current is a gain of about 11% in moisture content reduction, for said curve crosses the 12th hour ordinate at about 37% and the 8th hour ordinate at about 48%, showing that during the last period of 4 hours, the heated gas current is responsible for a reduction of 11% in the moisture content.

My invention does not exclude the application of high frequency electric power and simultaneously therewith a current of heated gas to lumber that has been partially dried by methods other than that herein set forth, namely, to kiln dried or air dried lumber, but, in such case, the lumber so dried is, generally speaking, somewhat discolored either by blackened pitch pockets or by fungus or mold requiring the planing of the surfaces of the lumber before it is generally useful. In this case, as in all variants of my process, the temperature of the heated gas to which the partially dried lumber is subjected simultaneously with the high frequency electric power treatment, should be low enough to prevent the temperature of the lumber due to the combined action of the electric power and heated gas from rising high enough to produce discoloration or distortion of the lumber, but, nevertheless, high enough to serve as an insulator for the heat produced in the lumber by the high frequency power, that is to say, high enough to prevent a substantial amount of the heat in the lumber from escaping into the ambient gas. While the time of producing commercial dried lumber in this manner is longer than that required by my preferred process, it is, nevertheless, much shorter than that required to reduce the moisture content of the lumber to the range of themoisture content of commercial dried lumber, viz., between 4% and 15%, by using the kiln drying method or the air drying method, without more. By the term stationary, as applied to the mass of lumber to be dried, I desire to be understood as meaning that there is no relative movement between the lumber and the electrodes 62,61, 68, in compartment 28, during the time the wood is being subjected to the high frequency power, as shown in the drawings selected to illustrate my invention.

Having thus disclosed my improved method and an illustrative embodiment of apparatus whereby the method may be practiced, without limiting myself thereto, what I claim and desire to secure by Letters Patent is:

1. In an apparatus for drying a large mass of completely enclosed green lumber by subjecting the same successively to a current of heated gas and to high frequency electric power, in combination, a heat insulated, continuous, longitudinally extending enclosure, movable and substantially air-tight end closures for the same, a substantially air-tight, movable partition intermediate said end closures for dividing said enclosure into two communicating compartments, each adapted to receive a trucklike carrier on which is loaded the lumber to be dried and to completely enclose such lumber, an electrode disposed between said carrier and the lumber, independent means for circulating a heated gas through each of said compartments, respectively, means actuated from the exterior of said enclosure for raising and lowering said partition, means for moving said carrier through said enclosure from the first of said compartments to the second when said partition is raised, the second of said compartments having a vertically movable electrode disposed near the top of said compartment and operable from the exterior thereof, each of said electrodes being substantially coextensive in area with the horizontal area of the mass of lumber to be dried, brushes secured to the second of said compartments and disposed in the paths of, and for electrical contact with, said electrodes, respectively, a source of high frequency electrical power and means electrically connecting said brushes .to said source of power.

2. In an apparatus for drying a large mass of completely enclosed green lumber by subjecting the same successively to a current of heated gas and to high frequency electric power, in combination, a heat insulated, continuous, longitudinally extending enclosure, movable and substantially air-tight end closures for the same, a substantially air-tight, movable partition intermediate said end closures for dividing said enclosure into two communicating compartments, each adapted to receive a trucklike carrier on which is loaded the lumber to be dried and to completely enclose such lumber, an electrode disposed between said carrier and the lumber, independent means for circulating a heated gas through each of said compartments, respectively, means actuated from the exterior of said enclosure for raising and lowering said partition, means for moving said carrier through said enclosure from the first of said compartments to the second when said partition is raised, the second of said compartments having a vertically movable electrode disposed near the top of said compartment and operable from the exterior thereof, a third electrode disposed intermediate the electrodes first mentioned, each of said electrodes being substantially coextensive in area with the horizontal area of the mass of lumber to be dried, brushes secured to the second of said compartments and disposed in the paths of, and for electrical contact with, said electrodes, respectively, a source of high frequency electrical power and means electrically connecting said brushes to said source of power.

3. In an apparatus for drying a large mass of completely enclosed green lumber by subjecting the sam successively to a current of heated gas and to high frequency electric power, in combination, a heat insulated, continuous, longitudinally extending enclosure, movable and substantially air-tight end closures for the same, substantially air-tight movable partitions intermediate said end closures for dividing said enclousre into a plurality of communicating compartments, each aparted to receive a trucklike carrier on which is loaded the lumber to be dried and to completely enclose such lumber, an electrode disposed between said carrier and said lumber, independent means for circulating a heated gas through each of said compartments, respectively, means actuated from the exterior of said enclosure for raising and lowering said partitions, respectively,

contact with, said electrodes, respectively, a

closure into two communicating compartments, I

each adapted to receive a trucklike carrier on which is loaded the lumber to be dried and to 16 completely enclose such lumber, an electrode disposed between said carrier and the lumber, in-

dependent means i'or circulating a heated gas through each 01' said compartments, respectively, means actuated from the exterior of said enclosure for raising and lowering said partition, means for moving said carrier through said enclosure from the first of said compartments to the second whensaid partition is raised, the second of said compartments having a vertically movable electrode disposed near the top of said compartment and operable from the exterior thereof, each of said electrodes being substantially coextensive in area with the horizontal area of the 12 mass of lumber to be dried, a source or high Irequency electrical power and means electrically connecting said electrodes respectively, to said source.

HAROLD P. WOOD.

REFERENCES CITED The following references are of record in the m file of thispatent:

UNITED STATES PATENTS Number Name Date 687,033 Kester Nov. 19, 1901 785,544 Emerson Mar. 21, 1905 1,147,593 Ayres July 20, 1915 1,161,587 Lyres Nov. 23, 1915 1,298,285 Bogaty Mar. 25, 1919 1,711,100 Payzant Apr. 30, 1929 1,867,546 Baer July 19, 1932 2,042,145 Darrah May 26, 1936 2,226,871 Nicholas Dec. 31, 1940 2,231,457 Stephen Feb. 11. 1941 2,307,344 Zottu Jan. 5, 1943 2,321,130 Crandell June 8, 1943 2,325,652 Bierwirth A118. 3, 1943 2,397,897 Wenger Apr. 2, 1946 2,408,434 Mann et al. Oct. 1, 1946 2,428,615 Brown Oct. 7, 1947 

